Sounds as if the clutch is slipping - this usually starts when you accelerate hard in a high gear, but this will get worse until it slips even in low gears.
If you bought this new, you may get a contribution from the dealer, but they may say this is "wear and tear" and due to the way you have driven it (for example, holding on the clutch on hills instead of neutral + handbrake or drag-race type starts from the lights).
If you bought it used, the previous owner may have maltreated it in those ways and worn the friction surfaces to the point where it slips, either way, the clutch probably needs to be replaced.
Edited by galileo on 20/08/2018 at 18:03
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